he is talking about driving it a total of 7 miles.
in a 1980's truck. So it might be electronic ignition and carbed, since efi wasn't standard till around 89 ish.
the starter would be the biggest draw.
keeping the blower motor off for heat and lights off 10 miles should not even be a sweat for a new battery.
disconnecting it prevents parasitic draws from draining the battery while sitting for x number of days.
more critical for newer cars but if he had something aftermarket on it, that could down it fast too.
radio's pull power to maintain radio station presets, alarms keep the alarm radio active so you can arm and disarm with the key fob, etc..